X-ray imaging apparatuses taking X-ray transmittance images are used in various fields of industrial and medical fields because the apparatuses can be used to non-destructively visualize the internal structures of objects to be measured (hereinafter referred to as objects). The contrast of an X-ray transmission image is caused by the differences in transmittance among X-rays transmitted through parts of an object. The transmittance of X-ray depends on the chemical composition of objects, the density of the objects, and the energies of the X-rays (i.e. the wavelength of the X-rays) that are used. Accordingly, in the case of using an X-ray apparatuses in related art, it is difficult to take legible high-contrast images of objects, such as soft materials or biological objects, mainly composed of light elements or fabricated by the objects and surrounding materials whose densities have small differences, because the objects have very high or similar X-ray transmittance.
X-ray imaging methods for detecting phase differences among X-rays are proposed (for example, refer to NPL 1) in order to measure high-contrast images of such objects. The phase difference appears as refraction in a portion having a density difference, for example, on an interface of a substance. In the method described in NPL 1, an object is irradiated by highly monochromatic X-rays and the intensity of the X-rays transmitted through the object is detected with an X-ray wedge-shaped attenuator. Specifically, the change in the amount of refraction angle of the X-rays through the object is detected as the change in the detected intensity to detect the phase difference in the method described in NPL 1. Since phase information on the X-rays (the amount of refraction of the X-rays) can be detected with the method described in NPL 1, it is possible to measure an image of high contrast.